Method for manufacturing multi-layered high-deformation piezoelectric actuators and sensors

Abstract

A method and apparatus for manufacturing prestressed piezoelectric actuators which maximizes output, and increases the precision and efficiency with which the multi-layer actuators are made. Individual layers of the piezoelectric actuators are automatically stacked and registered with respect to each other within press members prior to bonding the layers to each other with a thermoplastic adhesive. Compressive force is applied while heat is conductively transferred from a heating element to the actuator in order to raise the temperature of each of the layers above the melting point of the thermoplastic. The temperature of the heating element is then decreased until the temperature of the actuator layers drops to below the melting point of the thermoplastic adhesive, thereby bonding the layers. Compressive force is then released, and the actuators are removed, further cooled and polarized. The temperature of the actuator may be sensed, and the pressure and the heat applied to the actuator varied in accordance with the sensed temperature.

We claim: 
     
       1. A method of manufacturing a multilayered high deformation piezoelectric actuator, comprising the steps of: selecting a first piezoelectric ceramic layer, a first metal prestress layer and a second metal prestress layer, said first piezoelectric ceramic layer and said first metal prestress layer and said second metal prestress layer each having two major surfaces, wherein said second metal prestress layer has a dimension that is larger than the other layers;   placing in order in a press said first metal prestress layer, a first adhesive layer, said first piezoelectric ceramic layer, a second adhesive layer and said second metal prestress layer so as to form a stack comprising said first metal prestress layer, said first adhesive layer, said first piezoelectric ceramic layer, said second adhesive layer and said second metal prestress layer;   applying pressure to said stack with said press in a direction perpendicular to each of said major surfaces;   heating said stack to a temperature above a melting point of each of said adhesive layers and below a Curie temperature of said first piezoelectric ceramic layer;   maintaining a temperature of said stack above a melting point of each of said adhesive layers and below a Curie temperature of said first piezoelectric ceramic layer until each of said adhesive layers has melted;   after said step of maintaining the temperature of said stack, decreasing the temperature of said stack to below a melting point of each of said adhesive layers;   after said step of decreasing the temperature of said stack, releasing said pressure;   and, after said step of releasing said pressure, cooling said stack to room temperature; wherein said step of placing in order in a press said first metal prestress layer, a first adhesive layer, said first piezoelectric ceramic layer, a second adhesive layer and said second metal prestress layer comprises placing a first portion of said stack into a first recess within a first rigid press member and placing a second portion of said stack into a second recess within a said second rigid press member;   and wherein said second recess is configured to accommodate the difference in dimensions between said second metal prestress layer and said other layers.     
     
     
       2. The method according to claim 1, further comprising polarizing said piezoelectric ceramic layer after said step of cooling said stack. 
     
     
       3. The method according to claim 2, wherein said step of applying pressure to said stack comprises moving said first rigid press member toward said second rigid press member. 
     
     
       4. The method according to claim 3, wherein said step of heating said stack comprises raising a temperature of said press first press member or said second press member to above a temperature of said stack and conducting heat from said press to said stack. 
     
     
       5. The method according to claim 4, wherein said first adhesive layer is bonded to said first piezoelectric ceramic layer before said step of placing in order in a press said first metal prestress layer, a first adhesive layer, said first piezoelectric ceramic layer, a second adhesive layer and said second metal prestress layer. 
     
     
       6. The method according to claim 4, wherein said first adhesive layer is bonded to said first prestress layer before said step of placing in order in a press said first metal prestress layer, a first adhesive layer, said first piezoelectric ceramic layer, a second adhesive layer and said second metal prestress layer. 
     
     
       7. The method according to claim 4, further comprising sensing a temperature of said stack concurrently with said step of heating said stack. 
     
     
       8. The method according to claim 4, wherein said step of placing a first portion of said stack into the first recess within a first rigid press member and placing a second portion of said stack into the second recess within said second rigid press member comprises placing said first metal prestress layer into the first recess within said first rigid press member.